1. Field of the Invention
The present invention relates to a dental magnetic attachment utilizing amagnetic attraction force. More particularly, the present invention relates to a dental magnetic attachment in which a surface of a shell of a permanent magnet structure to be adhered and fixed to an alveolar ridge side of a denture base is beforehand processed so as to have a prescribed roughness, thereby enabling one to adhere and fix the permanent magnet structure within the denture base, with a stable holding power.
2. Description of the Conventional Art
As a method for setting a partial or complete denture within an oral cavity, in recent years, employed is a method utilizing a magnetic attraction force acting between a permanent magnet and a soft magnetic material. That is, this method is a method in which a keeper made of a soft magneticmaterial is fixedly set in an alveolar ridge portion within an oral cavity, whereas a permanent magnet structure is adhered and fixed in a position opposite to the keeper in an alveolar ridge side of a denture base, thereby enabling one to set a denture utilizing a magnetic attraction force acting between the keeper and the permanent magnet structure. According to this method, not only the denture can be set within the oral cavity without any hindrance in the function and esthetics of the denture, but also placement and removal to be carried out for the purpose of cleaning up the denture and the like are easy. Thus, application examples thereof are increasing rapidly.
In general, the setting of the denture using such a dental magnetic attachment is carried out in the following manner. That is, a root member of a keeper, which is fixedly set on a back surface of a flat plate made of a soft magnetic material positioning inside an oral cavity, by means of casting to embedded alloys or other methods, the keeper being formed so as to have a longitudinal section in an approximately T-shape, is embedded and fixedly set within a tooth root or artificial tooth root of residual teeth in an alveolar ridge portion in the oral cavity; a permanent magnet structure is adhered and fixed in a hole provided in a denture base positioning opposite to the keeper, by an adhesive or a self-curing resin, in the alveolar ridge side of the denture base; and during setting a denture within the oral cavity, a magnetic attraction force acts between the keeper and the permanent magnet to set the denture such that it is not dropped easily, while during the removal, it can be easily taken out by applying a larger power then the magnetic attraction force.
As the permanent magnetic structure of the dental magnetic attachment to be used in such a way, employed are generally those which accommodated a permanent magnet within the inside, the surrounding thereof being covered by a shell made of a corrosion-resistant soft magnetic or non-magnetic metal. In order to set the denture stably, the metal material that is used for the shell is required to have superior corrosion resistance for resisting to the corrosion in an environment within the oral cavity. Accordingly, in general, as the corrosion-resistant soft magnetic material, employed are ferrite-based stainless steels such as 16 xcx9c18Cr xe2x80x94bal Fe (SUS430), 17xcx9c20Crxe2x80x941.75xcx9c2.5Mo-bal Fe (SUS444), and 28.5xcx9c32.0Crxe2x80x941.5xcx9c2.5Moxe2x80x94bal Fe (SUS447J1), and austenite-based stainless steels represented by SUS316L. And, exemplified are those in which the corrosion-resistant metal material covers the permanent magnet structure except for a surface thereof coming contact with the keeper, or the whole surface of the permanent magnet structure in a thickness such that the magnetic attraction force between the permanent magnet structure and the keeper is not influenced.
The permanent magnet structure of the dental magnetic attachment is limited in terms of the size because it is adhered within the denture base. In general, a pillar having a diameter of about 3 to 4 mm and a height of about 1.5 to 2 mm, or an approximately square pillar having one side of about 2 to 3 mm and another side of about 3 to 4 mm and having a height of about 1.5 to 2 mm, is formed, and then adhered and fixed for use in a hole provided in the alveolar ridge side of the denture base of the completed denture. In this case, the works at the dental clinical or dental laboratories are often carried out in an environment where saliva or sebum from fingers, or other substances lowering the adhesive capacity are readily attached to the surface of the permanent magnet structure. In the case where the adhesion works to the denture base are carried out in the state that foreign matters are attached to the surface of the permanent magnet structure, the adhesive strength between the permanent magnet structure and the denture base is markedly lowered, leading to formation of a space between the permanent magnet structure and the denture base. In this case, when the space is large, the saliva or remnants of food or the like invade into the space, resulting in a hygienic problem. As the case may be, the permanent magnet structure is corroded. In a more severe case, there occurs a problem that the permanent magnet structure is dropped from the denture base.
This is considered to occur by the following matter. That is, the denture is used under severe conditions such as a condition under which a large stress is repeatedly applied to a part of the denture base by mastication, or a condition under which the denture is influenced directly by a temperature difference due to the contact with foods and drinks. Accordingly, the space is gradually formed during the use over a long period of time, and hence, the above-described problem is inevitable from occurrence.
Thus, as means for improving the adhesive strength, the manufactures give instructions to dentists or dental technicians to carry out the operation such that the surface of the permanent magnet structure must be surely cleaned during the adhesion; and in order to make the adhesive or self-curing resin easy to attach to the surface of the shell, after sandblast processing, the surface of the shell is subjected to primer processing and then adhered with the adhesive or self-curing resin. As means for preventing the dropping, with respect to the permanent magnet structure, there are applied various improvements for imparting mechanical retention forms such as protrusions or grooves to the side surface of the shell, as disclosed in Japanese Patent Laid-Open Nos. 54958/1992 and 150156/1996.
By taking these means, not only the improvement in adhesive properties of the permanent magnet structure to the denture base is devised, but also the permanent magnet structure is less dropped from the denture base due to the mechanical retention. However, as described above, for a dentist or a dental technician, uniform sandblast processing of an extremely small permanent magnet structure is a difficult to perform and a complicated operation requiring a skill. In the case where the sandblast processing is insufficient, a satisfactory effect for improving the adhesive properties is not likely attained sufficiently. On the other hand, when the sandblast processing is carried out excessively, the shell is likely bored, resulting in a problem such that the permanent magnet is exposed. In addition, there is a problem that a dentist or a dental technician who does not have a sandblast-processing unit cannot perform such processing.
Thus, the present invention is aimed to develop a dental magnetic attachment having a stable adhesive capacity, which does not require a dentist or a dental technician to perform sandblast processing during the use and does not form a space between a permanent magnet structure and a denture base even when it is used in an oral cavity over a long period of time, by beforehand processing a surface of a shell of the permanent magnet structure to be adhered and fixed to an alveolar ridge side of the denture base so as to have a roughness at which an adhesive strength can be most effectively enhanced.
In order to achieve the above-described aim, we, the present inventors made extensive and intensive investigations. As a result, it has been found that in the case where a surface of a shell of a permanent magnet structure except for a surface thereof coming contact with a keeper is beforehand processed by a chemical or physical method so as to have a surface roughness such that a maximum roughness is 5 to 15 xcexcm and that a ten-point average roughness is 3 to 8 xcexcm, a primer surely penetrates into irregularities formed on the surface, so that the metal surface is activated; a chemical bond between the metal surface and an adhesive to be applied thereafter is effectively brought, thereby enabling to impart a stable adhesive strength; and the irregularities formed on the surface act effectively to enhance a mechanical retention force, leading to accomplishment of the present invention.
Specifically, the dental magnetic attachment according to the present invention is a dental magnetic attachment, which comprises a keeper comprising a soft magnetic material to be fixedly set in an alveolar ridge portion within an oral cavity; and a permanent magnet structure having a permanent magnet aligned inside a shell to be adhered and fixed in a position of an alveolar ridge side of a denture base opposite to the keeper, wherein 80 to 100% of a surface of the shell of the permanent magnet structure except for a surface thereof coming contact with the keeper has a surface roughness such that a maximum roughness, Rmax is 5 to 15 xcexcm and that a ten-point average roughness, Rz is 3 to 8 xcexcm.